Jenkins Sidebar Link Plugin vulnerable to Path Traversal

Jenkins Sidebar Link Plugin allows specifying files in the userContent/ directory for use as link icons.

Sidebar Link Plugin 2.2.1 and earlier does not restrict the path of files in a method implementing form validation.

This allows attackers with Overall/Read permission to check for the existence of an attacker-specified file path on the Jenkins controller file system.

Sidebar Link Plugin 2.2.2 ensures that only files located within the expected userContent/ directory can be accessed.